Interplay of various loss mechanisms and ultimate size limit of a surface plasmon polariton semiconductor nanolaser

The issue of an ultimate size limit of a surface plasmon polariton (SSP) nanolaser is investigated by a systematic simulation study. We consider a prototypic design of a metal-insulator-semiconductor multi-layer structure with finite, varying lateral sizes. Our focus is on the design of such lasers operating at room temperature under the electrical injection. We find that there is an interesting interplay between the facet loss and the SPP propagation loss and that such interplay leads to the existence of a minimum-threshold mode in each mode group. The red-shift of the minimum-threshold mode with the decrease of device thickness leads to a further reduction of threshold gain, making the threshold for the SPP nanolaser achievable for many semiconductors, even at room temperature. In addition, we find that the threshold can be further reduced by using thinner metal cladding without much exacerbated mode leakage. Finally, a specific design example is optimized using Al0.3Ga0.7As/GaAs/Al0.3Ga0.7As single quantum well sandwiched between silver layers, which has a physical volume of 1.5 × 10-4 3 0 λ , potentially the smallest semiconductor nanolasers designed or demonstrated so far.